The present invention relates to methods for separating a metal from its metal oxide for analysis. The methods disclosed herein include approaches for providing a novel process for separating a metal from its water-soluble metal oxide in a pyrotechnic composition. Exemplary embodiments include a method of separation that allows for analysis of both metal and metal oxide using an elemental analysis technique, e.g., inductively coupled plasma optical emission spectrometry (ICP-OES) and determination of the relative amount of elemental metal and its oxide known as speciation.
Elemental boron is a commonly used pyrotechnic fuel with uses ranging from fireworks and airbags to defense and space exploration. However, boron is subject to oxidation by acids. The present invention is a method for distinguishing between elemental boron and the oxidized form H3BO3 (B(OH)3), developed to assess boron potassium nitrate (BKNO3), which is a widely-used initiator.
Generally, pyrotechnic compositions comprise a powdered metal and an oxidizer in intimate contact. An example of such a composition is boron potassium nitrate (BKNO3) where boron (B) is the fuel and nitrate (NO3−) in potassium nitrate (KNO3) is the oxidizer. If too much of the metal becomes oxidized, the pyrotechnic will not function as designed, nor will the device into which the pyrotechnic composition has been inserted function as designed. Exemplary devices using this exemplary pyrotechnic mixture include gas generators which are small ordnance devices within a reserve battery or on larger missiles, airbag actuators in automobiles, and squibs designed to perform various functions on systems, such as on a vehicle airbag system, or on a missile or a rocket. Because many of these devices are expected to sit for years before functioning properly, assessment of the speciation, (e.g., the relative amount of metal and metal oxide), is a critical measure for determining how long and under what conditions the devices can be expected to function reliably. The present invention solves the problem of obtaining an accurate, efficient, and commercially viable speciation via the methods described herein.
According to an illustrative embodiment of the present disclosure, an exemplary method first weighs a sample in digestion vials, adding water to dissolve the metal oxide out of the sample for a specific period of time at a specific temperature filtering the sample, and bringing the filtrate containing borate, potassium, and nitrate ions, (e.g., BKNO3), to a predetermined volume with an appropriate diluent. The filtration separates the water soluble oxide, (e.g., borate), from an elemental fuel, (e.g., boron). The residue is then digested by means of an appropriate digestant for a predetermined time at a predetermined temperature. The digested residue is then brought to a known volume with the same diluent material as was used with the filtrate. Next, both samples are ready for elemental analysis using a desired analytical technique used for detection of trace metals, (e.g., ICP-OES). A weight percent of both the elemental metal and the water-soluble oxide of that metal may then be computed using initial mass, and measured concentration of substances in both samples, (e.g., filtrate), digested water soluble oxide, and volume of each sample.
According to another illustrative embodiment of the present disclosure, the methods disclosed herein allow simultaneous analysis of metal and water-soluble metal oxide. According to a further illustrative embodiment of the present disclosure, exemplary methods disclosed herein may be used for assessment of shelf life of airbag actuators, namely the assessment of metal fuels other than boron with water-soluble oxides.
Additional features and advantages of the present invention will become apparent to those skilled in the art upon consideration of the following detailed description of the illustrative embodiment exemplifying the best mode of carrying out the invention as presently perceived.